ncall=-2 setup once per iteration of a given step for partials
ncall=-1 setup once per iteration of a given step for motion
ncall= 0 setup once per step
ncall= k evaluate acceleration for equation k.gt.0

the shadow coding has not been tested --since it is programmed
as a discontinuous effect (lamda=0 or 1) it has been found to
lead to numerical integration difficulties - hence it is
bypassed for now until more work is done with it ----l.f.